CN114342260A

CN114342260A - Capacitive sensor switch with optical sensor

Info

Publication number: CN114342260A
Application number: CN202080042596.5A
Authority: CN
Inventors: K·赫滕霍夫
Original assignee: Captron Electronic GmbH
Current assignee: Captron Electronic GmbH
Priority date: 2019-06-12
Filing date: 2020-05-20
Publication date: 2022-04-12
Also published as: EP3751739A1; EP3751739B1; US20220190827A1; WO2020249371A1; US11558053B2

Abstract

A sensor switch with water suppression includes a sensor electrode and a photodiode connected to an evaluation circuit. The evaluation circuit generates a capacitive sensor signal indicating that a conductive object is in the vicinity of the sensor switch and an optical sensor signal indicating that a light-opaque object is in the vicinity of the sensor switch. The capacitive sensor signal and the optical sensor signal are correlated to generate an output signal.

Description

Capacitive sensor switch with optical sensor

Technical Field

The present invention relates to a capacitive sensor switch that can be used to detect the proximity (proximity) of an object or body part, such as a hand, to a sensing surface, and a sensing and evaluation circuit thereof.

Background

A touch-sensitive switch for a cooktop is disclosed in US 8,823,393B 2. Here, an AC signal is coupled into the sensor board. An evaluation circuit measures the amplitude of the signal. If a human hand or another electrically conductive object is placed in close proximity to the sensor plate, a capacitive current flows between the sensor plate and the hand, thus reducing the amplitude of the AC signal. The evaluation circuit may comprise a threshold detector and a window comparator to detect certain changes in amplitude and issue a control signal at an output. A disadvantage is that a conductive liquid, such as water, on the sensor surface may have the same effect. Such liquids may therefore lead to false triggering of the switch.

Disclosure of Invention

The problem to be solved by the present invention is to provide a capacitive proximity sensor providing high immunity to false triggering by conductive liquids.

A solution to this problem is described in the independent claims. The dependent claims relate to further developments of the invention.

In an embodiment, a sensor switch includes a capacitive proximity sensor in combination with an optical sensor and an evaluation circuit. The capacitive proximity sensor comprises a sensor conductor or sensor electrode, which is typically a plate or foil of a conductive material forming the active sensor surface. It is preferably located at or near the bottom of the sensor switch housing. The electrode is connected to an evaluation circuit for evaluating and/or measuring the capacitance to ground. When a conductive object, such as a human hand that is in further contact with ground (e.g., standing on the floor), approaches the sensor electrode, the capacitance to ground increases. Instead of or in addition to ground, a reference electrode, which may be integrated into the sensor switch, may be used as a reference. The evaluation circuit itself has a capacitive or galvanic connection to ground, so that when a conductive object or body part approaches the sensor electrode, a change in capacitance can be detected. This can be measured, for example, by applying an AC or RF signal in the medium frequency range, preferably between 10kHz and 10MHz, to the sensor electrode while measuring the voltage at the sensor electrode. As the capacitance to ground increases, the voltage decreases. Here, the entire environment of the sensor switch may be considered as ground. If the evaluation circuit is sensitive enough, a very high impedance is sufficient to generate a detectable voltage drop and thus a low capacitance between the ground references of the evaluation circuit, which may for example be connected to the housing of the sensor switch to ground and through a person.

The optical sensor comprises at least one photosensor, such as a photodiode. It is preferred to use a photodiode as the photosensor, and thus the terms photosensor and photodiode are used synonymously. The photosensor may also include at least one of a photodiode, a phototransistor, or an integrated circuit. The at least one photodiode is preferably oriented in the direction of the active sensor surface and thus towards the top of the sensor housing. In a normal state, where no object touches the surface of the sensor, the photodiode will detect ambient light which may vary depending on the ambient conditions. For example, the ambient light may be very bright sunlight on a sunny day, artificial light in an industrial plant, or very dim light at night. If a person, i.e. a body part of such a person (preferably opaque), touches the switch, the level of light will be attenuated and thus a decrease of light can be detected. In the presence of water, which has a certain electrical conductivity and can attenuate the signal at the sensor electrode, so that the capacitive sensor signal is detected, the photodiode will find no or only a slight attenuation.

In order to allow a safe detection of the body part and to distinguish this from water, the signal of the sensor electrode and the signal of the photodiode have to be correlated and/or coincident. If the signal from the sensor electrode indicates a high attenuation and at the same time the photodiode indicates a high attenuation, the body part has approached the sensor with a very high probability. In such a case, a positive output signal (positive output signal) may be generated indicating a positive detection (positive detection). If only a capacitive sensor signal is present, but no optical signal is present, water or other conductive liquid may be present on the sensor, but no body part is present. Therefore, this event should be ignored. In the case of a signal change at the photodiode without increased attenuation at the capacitive sensor, there is a high probability that there is only an ambient light change, but no body part is approaching the sensor. Therefore, this event should also be ignored.

In this embodiment, the only positive events to be detected are reduced light intensity and reduced signal level at the capacitive sensor.

In another embodiment, there are a plurality of photodiodes that are used for optical proximity detection. Depending on the size and number of photodiodes, the size and location of the light-absorbing object in proximity to the sensor surface can be estimated. Thus, if the object is too small or too large, the event may be ignored. Thus, a conductive but light-absorbing liquid, such as dark water, can also be detected, since in most cases it will overflow the entire surface and thus cover a large number of photodiodes even if not all photodiodes. If there are a significant number of photodiodes evenly distributed over the sensor surface, the size of the object may be limited such that, for example, a finger covers a certain number of photodiodes, and if the number of photodiodes drops below a certain limit, the event will be ignored. Furthermore, an event may only be accepted if it is positively detected that the photodiodes have a certain spatial relationship, e.g. are close to each other. Conversely, if multiple photodiodes far apart from each other indicate higher attenuation, the event will be ignored.

There may also be certain sensitive and insensitive areas at the sensor surface, or certain areas that trigger certain events. For example, a two-pole sensor switch may be generated by grouping photodiodes of one half of the switches into a first group and photodiodes of the other half of the switches into a second group. A first event is triggered if a first set of photodiodes detects an event, and a second event may be triggered if a second set of photodiodes detects an attenuation. In another embodiment, a single photodiode may be used to optically identify a particular location on the switch. This may be one pole of a two pole switch.

In yet another embodiment, dynamic thresholds of capacitive sensors and/or optical sensors may be used. This may allow, for example, the detection of a finger in proximity to the sensor surface, even if the surface of the sensor is covered by water. In this case, the capacitive sensor signal is further increased, while the optical sensor signal also detects a higher optical attenuation.

In one embodiment, an evaluation circuit may be provided. The evaluation circuit may have a dynamic threshold to detect an increased electrical load at the at least one sensor electrode consistent with a decreased light level at the at least one photosensor.

In an embodiment, the evaluation circuit may be configured to store a dynamic threshold value based on the capacitive sensor signal when the optical sensor signal exceeds a predetermined threshold value. It may also be configured to generate an output signal when the capacitive sensor signal exceeds the dynamic threshold.

The dynamic threshold may be greater than the capacitive sensor signal.

In an embodiment, the evaluation circuit may be configured to store a dynamic threshold value based on the optical sensor signal when the capacitive sensor signal exceeds a predetermined threshold value. It may also be configured to generate an output signal when the optical sensor signal exceeds the dynamic threshold.

The dynamic threshold may be greater than the optical sensor signal.

The dynamic threshold may be derived from the sensor signal by multiplying the sensor signal by a constant factor and/or adding a constant offset. In another embodiment, at least one sensor electrode is planar and at least one photosensor is within the area of the at least one sensor electrode. There may be a distance between the sensor electrode and the photosensor that is less than half of the maximum extension of the sensor electrode. The distance may be less than 50mm, less than 20mm or less than 10 mm. The sensor electrode and the photosensor may be in a common plane, or in planes at a distance of less than 10mm, less than 5mm, or less than 2 mm.

In yet another embodiment, at least one LED is provided. The LED may be used for signaling (signal) a specific switch state, for illuminating the switch and/or for providing light to be detected by the photodiode. The LED may be turned off when the ambient light level is measured by the photodiode for signaling and illumination purposes. If the LED is used for measurement purposes, it should be lit up simultaneously when measuring a signal from at least one photodiode. There may be at least one or more pairs of LEDs and photodiodes that are preferably optically isolated from each other.

In one embodiment, the AC or RF signal may be in the frequency range of a few kHz to 5 MHz. The signal may have a rectangular or sinusoidal shape and is preferably a spread spectrum signal. Such a spread spectrum signal may be a sequential signal providing a pseudo-noise sequence. Different noise sequences may be used for different electrodes. This avoids any interference between adjacent electrodes.

In another embodiment, the sensor circuit may be implemented entirely or at least partially in a microcontroller. This provides lower cost and greater flexibility. Another embodiment relates to a method of detecting light-absorbing objects on a capacitive sensor surface by detecting incoming light reaching the sensor surface, preferably through a photodiode, and correlating the detected light signal with the capacitive sensor signal.

Drawings

The invention will be described hereinafter by way of example and not by way of limitation of the general inventive concept on the examples of embodiments with reference to the accompanying drawings.

Fig. 1 shows a top view of a sensor switch.

Fig. 2 shows yet another embodiment with grouped photodiodes and LEDs.

Fig. 3 shows a cross-sectional side view.

FIG. 4 shows a cross-sectional view of a sensor assembly.

Fig. 5 shows the basic functions.

Figure 6 shows a cylindrical embodiment.

Fig. 7 shows a first interleaved sensor embodiment.

Fig. 8 illustrates a second interleaved sensor embodiment.

Fig. 9 shows a schematic of a capacitive signal and an optical signal.

Fig. 10 shows a schematic diagram of a signal with dynamic threshold.

Fig. 11 shows a schematic diagram of a signal with dual dynamic thresholds.

Fig. 12 shows another evaluation system.

Fig. 13 shows a simple evaluation circuit.

Fig. 14 shows a more complex evaluation circuit.

Fig. 15 shows an even more complex circuit.

Fig. 16 shows the basic function of the sensor.

In fig. 1, a top view of the sensor switch 100 is shown. The sensor switch 100 has a housing 101 and a printed circuit board 210 carrying electronic components, such as a sensor electrode 162 and at least one photodiode 220. The printed circuit board 210 may also carry an evaluation circuit 150.

In fig. 2, yet another embodiment of a sensor switch 110 having grouped photodiodes and LEDs is shown. At least one LED 222 is disposed proximate to at least one of the photodiodes 220. The LEDs may be used to indicate some operational status of the switch to a person or operator of the switch. They may also be used to illuminate the switch itself so that the switch can be more easily identified or have a better appearance at night. Finally, LEDs may be used to generate light that may be detected by a photodiode for detecting the presence of a body part. This light can be used if the ambient light is insufficient. If the LEDs are used only for indication purposes or for illuminating the switch, they may be time-multiplexed (time-multiplex) so that the LEDs are off during the measurement interval when the photodiode measures ambient light for detecting the body part. If LEDs are used for detecting body parts, they must be illuminated during the measurement interval of the photodiode. The LEDs may be grouped with photodiodes or otherwise arranged as desired. The groups of LEDs and/or photodiodes may be optically isolated from each other to avoid cross-coupling of light. Isolation may also be achieved and/or improved by alternately turning such groups on and off.

In fig. 3, a cross-sectional side view is shown. The housing preferably has a cup shape for holding the circuit component. Preferably, the housing comprises a transparent material, such as glass, acrylic or PMMA. It may also comprise any translucent material and/or spectral filter. The components of the sensor may include a printed circuit board 210 holding at least a photodiode 220 and an optional LED 222. Near the top of the housing 101, there may be a diffuser film 240 that disperses light entering and exiting the transparent housing. This results in an optically smooth surface of the switch. The diffuser film may be held by springs 230.

In fig. 4, a cross-sectional view of the sensor assembly 160 is shown. At the bottom is a printed circuit board 210 that serves as a mechanical support for the sensor assembly. On the printed circuit board 210, there may be at least one photodiode 220 and at least one optional LED. Furthermore, there is also a sensor electrode, which may be one discrete layer, which may be a solid, a partially solid, a mesh, a ring or a plurality of wires. Alternatively, there may be a separate foil or grid on the printed circuit board. Above the sensor electrode 162 is a pad 164 of dielectric or conductive material. Preferably, the spacer has a recess above the photodiode so that light can penetrate the spacer. If the spacer is of a light-conducting material, no recess may be required. Above the spacer may be a diffuser film 166. This assembly may be used in a similar cup-shaped housing as shown in fig. 3.

In fig. 5, the basic functions are shown. Light source 800 generates ambient light. The light source may be the sun, a lamp, an LED or any other suitable light source. Light is radiated onto the sensor 110 and part of the light may be absorbed by a body part such as the finger 910, which is not transparent to light.

In fig. 6, a cylindrical embodiment is shown in a top view of sensor switch 250. The cylindrical housing 101 holds a circular sensor electrode 251, which preferably has a cut-out in its center. A photosensor 252 is positioned at this incision. The cut-out with the photosensor can also be in any other position. There may also be a plurality of photosensors. There may be at least one LED for providing light to the photosensor. This embodiment is very simple, robust and can be easily manufactured.

In fig. 7, a first interleaved sensor embodiment is shown in a top view of sensor switch 260. The first sensor electrode 261 and the second sensor electrode 262 are alternately arranged, wherein the first sensor electrode 261 has a U-shape and the second sensor electrode 262 has a T-shape and a base bar of the T-shape fits into the U-shape. Any one of the electrodes may be an (active) sensor surface, while the other electrode may serve as a reference or ground. Between the two electrodes, there is a photosensor 263. This sensor provides higher sensitivity and can cover a larger surface than a sensor with circular electrodes.

In fig. 8, a second interleaved sensor embodiment is shown in a top view of sensor switch 270. Here, the first sensor electrodes 271 and the second sensor electrodes 272 are alternately arranged. The second sensor electrode 272 has a plurality of fingers that fit into the grooves of the first sensor electrode 271. Any one of the electrodes may be an (active) sensor surface, while the other electrode may serve as a reference or ground. Between the two electrodes, there is a photosensor 263. This sensor provides much higher sensitivity and can cover a significantly larger surface than a sensor with circular electrodes. A greater number of fingers and grooves may also be present.

In the above embodiments, there may also be a plurality of photosensors. There may be at least one LED for providing light to the photosensor.

In fig. 9, a schematic of an exemplary capacitive signal and optical signal is shown.

The first diagram 310 shows a capacitive sensor signal, while a higher attenuation generates a higher signal value. Thus, in general, a conductive object or body part in proximity to the sensor electrode will cause an increase in the signal voltage. The signal is shown to the right along time axis 301 and to the top along voltage axis 302, with time increasing to the right and voltage increasing to the top.

The second schematic 320 shows the optical sensor signal resulting from light attenuation due to an object. Lower light attenuation and thus higher light levels result in lower voltages, while higher light attenuation and thus lower light levels result in higher voltages. Thus, in general, the proximity of a light-absorbing object or body part to the sensor electrode will result in an increase in the signal voltage.

A third diagram 330 shows the output signal of the switch.

In this example, when starting from left to right at the time axis 301, there is nothing on the sensor first, so that there is no body part close to the sensor and at least moderate ambient light is available. This results in a certain capacitive sensor signal 311, optical sensor signal 321 and output signal 331 of zero, indicating that no body part is detected. For example, when a finger is brought into close proximity to the switch, the attenuation of the capacitive sensor increases, resulting in a higher capacitive sensor signal 312. At the same time, the optical attenuation increases, further resulting in a higher optical sensor signal 322. As previously described, if there is positive capacitive detection and positive optical detection, the output signal will also be positive, resulting in output signal 332. Next, the finger is released, which again results in a capacitive signal 313 similar to the capacitive signal 311. Further, optical signal 323 falls back to a similar level as signal 321, and thus, the output signal goes to zero, indicating that there is no body part proximity switch. It is noted that the optical sensor signal has some ripples on the curve, since the ambient light may change due to various influences in the space around the sensor, such as a person walking around within a distance of one or several meters, or a deviation or change of the light source. More intense light changes may also occur, such as a peak 324 caused by optical distortion of some light-absorbing object located between the light source and the switch, but not entering the close proximity switch. Thus, the capacitive sensor signal remains in the low state 313 and thus the output signal also remains in the low state 333, indicating that no body part is in close proximity to the switch.

In another case, not shown here, water may be present on the sensor. Then, there may be a higher capacitive sensor signal due to the conductivity of the water, but the optical sensor signal will remain low due to the optical transmittance of the water. Therefore, the output signal will be zero.

Fig. 10 shows a schematic diagram of a signal with a dynamic threshold circuit. In this embodiment, a photosensor is used to define the sampling time for the dynamic threshold of the capacitive sensor. The signal is similar to the previous figure, but there is now a dynamic threshold for the capacitive sensor signal. A first schematic 340 shows a capacitive sensor signal. A second diagram 350 shows the optical sensor signal. The third diagram 360 shows the output signal.

First, the capacitive sensor signal 340 is described. Before finger contact, a dynamic threshold 344 is generated from the capacitive sensor signal 341. Preferably, the threshold value is offset or proportional to the sensor signal or offset or proportional to the sensor signal above the sensor signal. When, as will be explained later, the optical sensor signal 352 exceeds the threshold 354 at time 355, a hold signal may be issued and the dynamic threshold 344 will be stored at value 345. Alternatively, the capacitive sensor signal 341 may be stored and its threshold may be calculated. As the finger approaches the sensor further, the capacitive sensor signal may further add to the sensor signal 342. When this sensor signal 342 increases above the stored threshold at time 347, an output signal 362 is generated until the sensor signal 342 drops below the stored threshold at time 348. At a later time, when the optical sensor signal 353 after finger contact falls below the threshold 354, the hold on the threshold is released and the dynamic threshold 346 tracks the capacitive sensor signal 343 again after finger contact. In an embodiment, output signal 362 is entirely dependent on sensor signal 342 staying above threshold 345. The optical sensor signal 352 may fall below the threshold 354 without affecting the output signal 362. In another embodiment, the output signal 362 may be set to zero when the optical sensor signal 352 falls below the threshold 354.

Now comes to the optical sensor signal 350. Prior to finger contact, the optical sensor signal 351 is typically below the static optical sensor threshold 354. When a finger, body part, or another object approaches the sensor, the signal adds to the optical sensor signal 352 upon finger contact, which optical sensor signal 352 may exceed a threshold 354. When the optical sensor signal 352 exceeds the threshold 354 at time 355, a hold signal may be issued and the dynamic threshold 344 will be stored. When the object leaves the sensor switch, the optical sensor signal 352 becomes a lower signal 353 and drops below the threshold 354 at time 356. The dynamic threshold 344 will then be released so that it tracks the capacitive sensor signal.

Finally, the output signal 360 is depicted. The signal is at

low levels

361, 363 before and after finger contact. During finger contact, the output signal is at a high level 362 when the sensor signal 342 is above a stored threshold 345, coinciding with the optical sensor signal 352 above a threshold 354 for at least a certain time.

The device and procedure as described above provide a high immunity to false alarms. It is based on the fact that: generally, a photosensor detects the presence of an object earlier than a capacitive sensor. Therefore, a photosensor is used to define a threshold for a capacitive sensor.

In one embodiment, the functions of the capacitive sensor and the optical sensor may be interchanged such that curve 340 is related to the optical sensor signal and curve 350 is related to the capacitive sensor signal.

FIG. 11 shows a schematic diagram of a signal with a dual dynamic threshold circuit. In this implementation, the signal of the photosensor is associated with a capacitive sensor. The signal is similar to the previous figures, but there are now dynamic thresholds for the two sensor signals. A first schematic diagram 370 shows a capacitive sensor signal. The second schematic 380 shows the optical sensor signal. A third schematic 390 shows the output signal.

First, the capacitive sensor signal 370 is described. The capacitive sensor signals (first capacitive sensor signal 371, second capacitive sensor signal 372, third capacitive sensor signal 373, fourth capacitive sensor signal 374, and fifth capacitive sensor signal 375) are compared to dynamic thresholds (first capacitive sensor threshold 376, second capacitive sensor threshold 377, third capacitive sensor threshold 378, and fourth capacitive sensor threshold 379). The sampling signals (first sampling signal 394, second sampling signal 395, third sampling signal 396, and fourth sampling signal 397) may be generated whenever the sensor signal exceeds a dynamic threshold. Such a sampled signal may also be generated if the sensor signal becomes below the dynamic threshold by a certain amount. From such a sampled signal, a new threshold is generated by increasing or decreasing the threshold, such as described in the above embodiments. Here, a fourth capacitive sensor signal 374 is generated due to the proximity of a finger or other detectable object to the sensor.

The optical sensor signal 380 is now described in more detail. The optical sensor provides optical sensor signals (first optical sensor signal 381, second optical sensor signal 382, third optical sensor signal 383, fourth optical sensor signal 384, and fifth optical sensor signal 385), wherein the fourth optical sensor signal 384, which has a higher level than the other sensor signals before and after the optical sensor signal, is caused by the proximity of a finger or other detectable object. Each time a sampling signal is generated, a new threshold (first optical sensor threshold 386, second optical sensor threshold 387, third optical sensor threshold 388, and fourth optical sensor threshold 389) is generated by increasing or decreasing the sensor signal based on the sensor signal, such as described in the above embodiments. In yet another embodiment, the threshold may be an average of the optical sensor signal over a past period, e.g., over a predetermined period of time or since the last sampled signal. Furthermore, when the sampling signal is generated, the value of the optical sensor signal is compared with the threshold value before the new threshold value is generated. If the optical sensor signal exceeds the threshold by a predetermined amount, output signal 392 is generated.

Finally, output signal 390 is depicted. The signal is at

low levels

391, 393 before and after the finger contact. During finger contact, when the fourth capacitive sensor signal 374 generates the third sampled signal 396 and the optical sensor signal 384 exceeds the threshold value 389 by a predetermined amount, the output signal is at a high level 392.

The apparatus and procedure as described above provide increased immunity to false alarms. It is based on the fact that: generally, a photosensor detects the presence of an object earlier than a capacitive sensor. Therefore, a photosensor is used to define a threshold for a capacitive sensor.

In one embodiment, the functions of the capacitive sensor and the optical sensor may be interchanged such that curve 370 is related to the optical sensor signal and curve 380 is related to the capacitive sensor signal. Fig. 12 shows another evaluation system. The diagram 410 shows a capacitive sensor signal and an optical sensor signal, with higher attenuation generating higher signal values. Capacitive sensor values are labeled along a horizontal axis 401, while optical sensor values are labeled along a vertical axis 402. In the sampling case, the curve may start at the lower left corner with low values for the capacitive sensor and the optical sensor. When the value of the optical sensor value first increases due to the proximity of a finger or other detectable device, the curve moves upward. Later, the capacitive sensor value may increase, which results in a curve that moves to the right. A high or positive output signal is generated when said value exceeds a certain predetermined limit curve 412, preferably illustrated by a positive detection area 413. When the object is removed, the curve returns to the lower left corner as the starting position. In an alternative embodiment, a third axis representing time may be used. This may lead to dynamic switching characteristics.

In fig. 13, a simple evaluation circuit 700 is shown. It has two inputs. The first input comprises a photodiode 220, which is only symbolically shown here. Additional required circuitry, such as biasing circuitry and/or amplifiers, is not shown. At the second input there is a sensor electrode 180, preferably a sensor electrode as previously shown. It is only symbolically shown here. Further required circuitry, such as signal generator circuits and/or amplifiers and/or detection means, are not shown. By approaching the body part of the sensor, it bridges with a relatively high impedance to ground, to which the sensor circuit is also referenced.

The signal of the photodiode 220 and the signal of the sensor electrode 180 are each filtered by a band pass filter 701 to remove unwanted noise and distortion. Although both band pass filters have the same reference numerals, they may have different band pass characteristics suitable for the photodiode signal path or the capacitive signal path. After the bandpass filter 701, a threshold detector 702 may be present to distinguish whether the input signal is above or below a certain threshold level. The output signal of the threshold detector is coupled by an and gate 703 which generates a positive output signal 709 only when there is a positive capacitive detection and a positive photo detection.

In fig. 14, a more complex second evaluation circuit is shown. It is based on the circuit of fig. 7. Here, a low pass filter 704 is added to each threshold detector 702. The low pass filter 704 generates a threshold signal 705 for the threshold detector and thus provides a dynamic switching threshold. This gives the circuit a significantly higher dynamic range, which is particularly useful for varying ambient light conditions. Therefore, it may be sufficient to implement such a low pass filter only at the light detection path coupled to the photodiode 220. This dynamic threshold allows a reliable distinction between conductive liquids or body parts such as fingers. Even a sensor in which the liquid is distributed over the sensor surface can detect the finger, because the liquid only shifts the threshold to a slightly higher level. The finger will cause a further increase in the signal level, which can now be detected by such a dynamic threshold circuit. In one embodiment, this circuit may be made to operate as described in FIG. 10.

In fig. 15, a more complex third evaluation circuit is shown. This evaluation circuit is based on the evaluation circuit of the previous figure. In this circuit, a dynamic threshold control 706 is provided. In one embodiment, this circuit may be made to operate as described in FIG. 11.

In fig. 16, the basic function of the sensor is shown. A person 900 standing on a floor substantially referenced to ground 190 touches the sensor 100. The signal of the sensor signal 100 is evaluated by an evaluation circuit 150 and an output signal 151 is generated. The evaluation circuit 150 is referenced back to the same ground 190 through its housing and environment, as where a person is located. In an alternative embodiment, the signal may be referenced to a ground electrode at the sensor 100 or a ground electrode of the sensor 100, rather than to the ground 190.

List of reference numerals

100 sensor switch

101 casing

110 sensor switch

150 evaluation circuit

151 output signal

160 sensor assembly

162 sensor electrode

164 shim

166 diffuser film

180 sensor electrode

190 to ground

210 printed circuit board

220 photodiode

222LED

230 spring

240 diffuser film

250 cylindrical sensor switch

251 sensor electrode

252 photoelectric sensor

260 staggered sensor switch

261 first sensor electrode

262 second sensor electrode

263 photoelectric sensor

270 second interleaved sensor switch

271 first sensor electrode

272 second sensor electrode

273 photoelectric sensor

301 time axis

302 voltage axis

310 capacitive sensor signal

311 capacitive sensor signal before finger contact

312 capacitive sensor signal upon finger contact

313 capacitive sensor signal after finger contact

320 optical sensor signal

321 optical sensor signal before finger contact

322 optical sensor signal upon finger contact

323 optical sensor signal after finger contact

324 optical sensor signal with optical distortion

330 output signal

Output signal before 331 finger contact

332 output signal at finger touch

333 output signal after finger contact

340 capacitive sensor signal

341 capacitive sensor signal before finger contact

342 finger contact

343 capacitive sensor signal after finger contact

344 dynamic threshold before finger contact

345 stored threshold value

346 dynamic threshold

Time for which 347 capacitive sensor signal exceeds threshold

348 time for capacitive sensor signal to fall below threshold

350 optical sensor signal

351 optical sensor signal before finger contact

352 optical sensor signal upon finger contact

353 optical sensor signal after finger contact

354 static optical sensor threshold

355 time for optical sensor signal to exceed threshold

356 time for optical sensor signal to fall below threshold

360 output signal

361 output signal before finger contact

362 output signal at finger touch

363 output signal after finger contact

370 capacitive sensor signal

371 first capacitive sensor signal

372 second capacitive sensor signal

373 third capacitive sensor signal

374 fourth capacitive sensor signal

375 fifth capacitive sensor signal

376 first capacitive sensor threshold

377 second capacitive sensor threshold

378 third capacitive sensor threshold

379 fourth capacitive sensor threshold

380 optical sensor signal

381 first optical sensor signal

382 second optical sensor signal

383 third optical sensor signal

384 fourth optical sensor signal

385 fifth optical sensor signal

386 first optical sensor threshold

387 second optical sensor threshold

388 third optical sensor threshold

389 fourth optical sensor threshold

390 output signal

391 output signal before finger contact

392 output signal at finger contact

393 output signal after finger contact

394 first sampled signal

395 second sampling signal

396 third sampled signal

397 fourth sample signal

401 capacitive sensor value

402 photosensor value

410 schematic of sensor values

Curve of 411 sensor values

412 limit curve

413 positive detection area

700 first evaluation circuit

701 bypass filter

702 threshold detector

703 AND gate

704 low-pass filter

705 threshold signal

706 dynamic threshold control device

709 output signal

710 second evaluation circuit

800 light source

900 people

910 finger

Claims

1. Sensor switch (100) comprising at least one sensor electrode (180) and at least one photosensor (220), both connected to an evaluation circuit (700), wherein the evaluation circuit is configured to:

-generating a capacitive sensor signal (310) indicating that a conductive object is in the vicinity of the sensor switch (100),

-generating an optical sensor signal (320) indicating that a light-tight object is in the vicinity of the sensor switch (100),

-generating an associated output signal indicating that a light-tight, electrically conductive object is in the vicinity of the sensor switch (100) from the capacitive sensor signal (310) and the optical sensor signal (320)

It is characterized in that the preparation method is characterized in that,

the evaluation circuit (700) has a dynamic threshold to detect an increased electrical load to the at least one sensor electrode (180) consistent with a decreased light level at the at least one photosensor (220).

2. The sensor switch (100) of claim 1,

it is characterized in that the preparation method is characterized in that,

the evaluation circuit (700) is configured to generate an output signal in dependence of an electrical load to the at least one sensor electrode (180).

3. The sensor switch (100) of any one of the preceding claims,

it is characterized in that the preparation method is characterized in that,

the evaluation circuit (700) is configured to generate an output signal in dependence on the light level at the at least one photosensor (220).

4. The sensor switch (100) of any one of the preceding claims,

it is characterized in that the preparation method is characterized in that,

the evaluation circuit (700) is configured to store a dynamic threshold value (345) based on the capacitive sensor signal (310) when the optical sensor signal (320) exceeds a predetermined threshold value (354).

5. Sensor switch (100) according to the preceding claim,

it is characterized in that the preparation method is characterized in that,

the evaluation circuit (700) is configured to generate an output signal when the capacitive sensor signal (310) exceeds the dynamic threshold (345).

6. The sensor switch (100) of claim 4,

it is characterized in that the preparation method is characterized in that,

the dynamic threshold (345) is greater than the capacitive sensor signal (310).

7. The sensor switch (100) of any one of claims 1 to 3,

it is characterized in that the preparation method is characterized in that,

the evaluation circuit (700) is configured to store a dynamic threshold value (345) based on the optical sensor signal (320) when the capacitive sensor signal (310) exceeds a predetermined threshold value (354).

8. Sensor switch (100) according to the preceding claim,

it is characterized in that the preparation method is characterized in that,

the evaluation circuit (700) is configured to generate an output signal when the optical sensor signal (320) exceeds the dynamic threshold (345).

9. The sensor switch (100) of claim 7,

it is characterized in that the preparation method is characterized in that,

the dynamic threshold (345) is greater than the optical sensor signal (320).

10. The sensor switch (100) of any one of the preceding claims,

it is characterized in that the preparation method is characterized in that,

the at least one sensor electrode (180) is planar and the at least one photosensor (220) is within the area of the at least one sensor electrode (180).

11. The sensor switch (100) of any one of the preceding claims,

it is characterized in that the preparation method is characterized in that,

the at least one photosensor includes at least one of a photodiode, a phototransistor, or an integrated circuit.

12. The sensor switch (100) of any one of the preceding claims,

it is characterized in that the preparation method is characterized in that,

at least one LED (222) is provided and configured for at least one of: signaling a switch state, illuminating a switch, or providing light to the photosensor.

13. A method of detecting light-absorbing objects on a capacitive sensor surface by detecting incoming light reaching the sensor surface and correlating the detected light signal with the capacitive sensor signal.

14. The method of claim 13, wherein the first and second light sources are selected from the group consisting of,

it is characterized in that the preparation method is characterized in that,

use of a capacitive sensor switch according to any of claims 1 to 12.